The present invention relates generally to electrophographic copying machines and more particularly to a device for cleaning the photosensitive members of such machines.
In electrophotographic copying machines of the toner image transfer type, the surface of the photosensitive member must be cleaned to remove the toner which remains thereon after a toner image formed on the surface has been transferred to copy paper. Devices for cleaning the photosensitive surface, are known. One such known device includes an elastic blade adapted to be held in pressing contact with the surface of the photosensitive member to wipe the surface clean. U.S. Pat. No. 3,859,691, for example, discloses a device of this type which, as shown in FIG. 1 of the accompanying drawings, which will be described more fully hereinafter, includes an elastic blade B supported at its upper base portion by a holder A and held in pressing contact with the surface of a photosensitive member D which rotates in the direction of arrow C. The blade B is inclined at an obtuse angle .theta..sub.1 with that surface of the member D which is located on the side of the blade facing opposite to the direction of rotation of member D so that end portion b will clean member D. Since the blade B is adapted to be placed into the holder A while its open end a is facing down, the blade B must be inserted into the holder A with care to prevent the blade from falling. Holder A must also be designed to firmly retain the blade B in order to prevent the blade B from slipping out of the holder A while it is being brought into position for contact with the surface of the photosensitive member D. This known device also has the disadvantage that during the rotation of the photosensitive member D and while the blade B is cleaning the photosensitive surface, the blade end portion b has a tendency to curl up toward the direction of rotation of the photosensitive member D as a result of frictional contact with the surface of the member D, thus failing to perform the desired cleaning operation.
FIG. 2 of the accompanying drawings shows another blade B which extends upward while being supported by a holder A. This general arrangement is more fully disclosed in U.S. Pat. No. 3,552,850. In this arrangement the bottom surface of blade B (facing opposite the direction of rotation of member D) is held in pressing contact with the surface of a photosensitive member D and is inclined at an acute angle .theta..sub.2 with the surface of the member D located on that side of the blade facing opposite to the direction of rotation of member D. Although the blade of this type is not likely to fall, the frictional force F between the forward end portion b of the blade B and the photosensitive member D acts to draw the blade B out of the holder A while the blade cleans the surface of the member D. Thus the holder A, like the one shown in FIG. 1, must be designed to fully and rigidly hold the blade B to prevent it from coming out. Additionally, the resultant force R of the normal reaction N exerted on the blade B by the surface of the photosensitive member D and the frictional force F between the blade B and the member D acts to move the blade end portion b away from the photosensitive surface, thus reducing the pressing force of the blade B on the photosensitive member D. Consequently, the blade B might leave residual toner partially unremoved because of its reduced cleaning ability.
The blade B shown in FIG. 3 of the accompanying drawings appears useful for overcoming the disadvantages of the conventional devices described above. This blade B is held in pressing contact with the surface of a photosensitive member D and is positioned laterally at an angle .theta..sub.3 with the surface of the member D located on that side of the blade facing opposite to the direction of rotation of the photosensitive member D. The angle .theta..sub.3 is almost as large as a right angle. This arrangement is free of the drawback of the device shown in FIG. 1 that the blade B, when extending downward, is likely to fall or to be curled up by frictional contact with the photosensitive surface. The arrangement of FIG. 3 has also overcome the drawback of the device of FIG. 2 that the blade B might be drawn out of the holder by frictional contact with the photosensitive surface or the blade B is unable to fully remove the residual toner because the blade bears on the photosensitive surface under reduced pressure with a lower frictional force acting between the blade and the photosensitive member D.
However, since the angle .theta..sub.3 is approximate to a right angle, the blade B is almost unable to elastically contact the photosensitive member D and acts thereon as if it were a non-elastic body. As a result, the contact effected between the blade B and the photosensitive member D is not as intimate as required to overcome the minute projections on the opposed contact surfaces such as illustrated in FIG. 4. When the photosensitive member D axially deflects as shown in FIG. 5, or when the contact face of the blade B deflects as shown in FIG. 6, as a result of an error involved in mounting or shaping the blade B, the blade will be unable to intimately contact the photosensitive surface across its full length by absorbing the deflection with its flexibility. In either case therefore, the blade B will not evenly contact the photosensitive member D and a gap G will be formed therebetween as shown in FIGS. 4 to 6. The surface of the photosensitive member will therefore not be effectively cleaned.
This defect can be eliminated solely by pressing the blade B against the photosensitive member D in the direction of arrow E with an increased force. The frictional force between the blade B and the member D will then increase in proportion to the increase of the pressing force, necessitating a greater torque for the rotation of the member D and causing rapid wear or damage to the photosensitive surface or to the contact end portion b of the blade B.